Severe obesity is an increasingly prevalent chronic condition that is difficult for physicians to treat in their patients through diet and exercise alone. Generally, gastrointestinal surgery promotes weight loss by restricting food intake, and more specifically, restrictive operations limit food intake by creating a narrow passage or “stoma” from the upper part of the stomach into the larger lower part, which reduces the amount of food the stomach can hold and slows the passage of food through the stomach. Initially, the stoma was of a fixed size, but physicians have more recently determined that the procedure is more effective if the stoma can be adjusted to alter its size. One of the more commonly used of these purely restrictive operations for obesity is adjustable gastric banding (AGB).
In an exemplary AGB procedure, a hollow band (i.e., a gastric band) made of silicone elastomer is placed around the stomach near its upper end, creating a small pouch and a narrow passage (i.e., a stoma) into the rest of the stomach. The band is then inflated with a saline solution by using a non-coring needle and syringe to access a small port that is placed under the skin. To control the size of the stoma, the gastric band can be tightened or loosened over time by the physician or another technician extracorporeally by increasing or decreasing the amount of saline solution in the band via the access port to change the size of the passage or stoma. One such exemplary gastric band system is the BioEnterics® LAP-BAND® System available from Allergan Medical of Irvine, Calif.
After a port has been placed in a patient, it is often difficult to locate the port, and to support insertion of a needle. The technician or physician who is injecting or withdrawing saline needs to locate the center of the port. Typically the physician palpitates the area to determine the general location of the port and then pinpoints its location by probing the area with a hypodermic needle. This can lead to multiple needle sticks and/or a failure to find and access the port. The location process is complicated as the port is typically positioned beneath other tissue such as fat.
In some cases, port location is accomplished through the use of X-rays and or fluoroscopes. However, these technologies are expensive to use, require an additional technician to operate the location equipment, and may require the port to be manufactured with materials that are more suited for locating but that are less biocompatible. As a result, the medical industry continues to demand less complex and costly devices and methods for locating the inflation/deflation port for adjustable gastric band systems while requiring that the port locating devices be accurate and relatively easy to use.
Additionally, with implantable medical devices (IMDs), it is often desirable to be able to read data from the IMD and, in some cases, to write data to the IMD. For example, medical device developers have created IMDs that include passively powered radio frequency (RF) transponders and these transponders are powered to communicate with an external transmitter/receiver. The passive RF device has programmable memory for storing information related to the device and/or the patient. For example, the information may include patient demographics, implant data, and manufacturer or device information (e.g., manufacturer ID, IMD model, serial numbers, and the like). In other cases, sensors are provided with the IMD to obtain patient information such as blood pressure, and the sensor collected data is transmitted from the IMD to an external transmitter/receiver device.
Some of these RF-based devices require the transmitter/receiver to be held within a relatively close distance of the implanted device to obtain accurate signals from the IMD. Efforts have been made by developers to measure the quality of the RF signals received from the transponder on the IMD to determine when the transmitter/receiver is within an acceptable range of the IMD transponder, and an audio signal may be used to indicate an acceptable relative distance between the two devices. However, the determination that an IMD and a transmitter/receiver are within a particular distance from each other is not satisfactory for inserting a needle into a center of a gastric band port where the accuracy required is measured in millimeters.
Hence, there remains a need for an improved method and system for locating a center of an inflation/deflation or “access” port of a gastric band after it has been implanted within a patient or for locating another implanted IMD accurately. Preferably, such a method and system would provide effective feedback to a technician or physician attempting to insert a needle within the center of the access port so as to facilitate accurate insertion of the needle. Further, it is preferable that such a method and system be compatible with reading data from the access port (or other IMD) and, in some cases, for writing data to the access port (or other IMD).